The present invention relates to a magneto-optic recording/reproducing apparatus which records and reproduces a video signal by the use of a magneto-optic recording disk, and more particularly to an improvement for detecting a defect contained in a magneto-optic recording disk.
By utilizing a magneto-optic recording disk, a video signal and a data signal are conventionally recorded and reproduced. In recording/reproducing operation of the magneto-optic recording disk, magneto-optical effects known as the Kerr effect and the Faraday effect are utilized. Namely, in a recording process, a magnetized condition of a magneto-optic recording medium on the disk surface is changed in accordance with the state of a signal, while, in a reproducing process, a signal having a level corresponding to the magnetized condition is extracted. With regard to a magneto-optic recording disk, it is customary to contain defects on the disk surface. Therefore, in a magneto-optic recording/reproducing apparatus, signal noise or a signal dropout portion associated with such disk defect is detected and compensated by signal processing. This compensation is well known as dropout compensation in the field of video tape recording/reproducing.
Defects in a magneto-optic recording disk are usually classified as dust that adheres to the disk in its manufacturing process, and unevenness of a recording layer, that occurred in the process of its formation by sputtering. In the area of defective parts on the disk, the reflective ratio is different from that of normal parts. Generally, the reflective ratio is greater if the defect is dust, or is lower if it is unevenness. In a typically available magneto-optic recording disk, most defects are derived from dust and are on the order of tens of microns in size. Further, defects of hundreds of microns or larger in size, which are derived from unevenness, are also contained.
In a conventional magneto-optic recording/reproducing apparatus which processes a video signal with frequency modulation, only the larger size defects in the order of hundreds of microns or above are detected from a reproduced video signal and signal compensation is performed on the basis of the defect detection.
In other words, conventionally, most of the small size defects on the magneto-optic recording disk are not detected and therefore the level of signal compensation is sufficient. As a result, it is impossible to produce a video signal of high resolution or of high quality.